Compost construction 101

Even with perfect management, dairy cows and calves die. They have a finite lifespan. And in the real-world absence of flawless management, animals are also susceptible to disease, accidents and human error. Those that expire before heading to the sale barn or slaughterhouse must be dealt with in an environmentally responsible fashion that fits the economics of your dairy.

It used to be free, or at least less expensive, to get rid of dead livestock. Sometimes you could even make a few dollars on animal carcasses. But rendering services are not cheap anymore — if they are even an option.

Composting animal carcasses can provide a cost-effective disposal method, especially since you can create composting facilities with minimal investment. And the process can be an environmentally friendly alternative to burial, a common on-farm solution that is prohibited in some states and geographic locales due to water quality concerns.

Follow these steps to design and build a composting facility for your dairy. The steps were developed with the help of Jay Harmon, Iowa State University extension ag engineer; Dan Short, University of Wisconsin extension livestock agent in Dodge County, Wis.; and Mike Looper, USDA-Agricultural Research Service research animal scientist based in Booneville, Ark.

1. Select your site.

Use these criteria to determine the right spot for your compost pile.

The site must be high and dry, easily accessible in all weather, and allow plenty of room in which to maneuver equipment. Equipment will be used to deliver animals, turn compost material and load completed compost material for field application.

Locate your compost facility away from all animals on the dairy. Consider daily dairy traffic patterns so that you don’t track compost material from the site to animal pens and compromise biosecurity.

Place it at least 100 feet away from surface water, wells or other ground-water conduits. (Requirements vary by location, so check with your local Natural Resources Conservation Service or state agriculture department.)

Provide good drainage to prevent pooling. A 1 percent to 3 percent slope is ideal. Just be sure the area doesn’t drain into surface water. If this is a concern, add a 1-foot to 2-foot berm around the compost site to keep runoff from escaping.

If possible, keep piles hidden, or at least in limited view of your neighbors and passing motorists. If you can’t keep it out of plain sight, keep the site well-groomed or even landscaped.

2. Size your facility.

Start by determining your mortality rate. This tells you approximately how many animals you’ll have to accommodate annually. For example, a 1 percent to 2 percent mortality rate on a 2,000-cow dairy means you’ll have to handle 20 to 40 cows in your compost facility. Also factor in calf mortality — if you raise your own calves — so you know the total number of animals you must compost.

Next, estimate how much room you’ll need. In general, each animal requires the space it takes up, plus it must be surrounded by 1 foot of carbon material — such as sawdust or chopped straw — all the way around. And the base of the pile must contain 1 to 2 feet of carbon material before any animals are placed there. Keep in mind carcasses will compress this material.

The maximum pile height is about 6 feet. However, depending on your mortality loss, and how much space you have available, you may not need a pile that high.

The best width for compost piles and piles within bins is 12 to 15 feet wide.

So, given a maximum height of 6 feet, and an optimum width of 12 to 15 feet, all that is left to determine is pile length. You must leave at least 6 inches between carcasses, so overall length depends on how many animals you must compost and their size.

Likewise, the number of composting bins you put in a permanent structure also depends on these factors. If you choose a permanent structure, be sure to leave enough room for your front-end loader to access the pile. Also make sure doors, alleys and compost bins are wide enough to allow equipment entry.

3. Select your system.

Determine whether you want a permanent structure, a temporary structure made from low-quality hay or straw bales, or a compost windrow. Your facility can be as elaborate, or as economical, as your needs mandate.

Each system can be used successfully in most areas of the country throughout all four seasons, and each works on the same basic principle of accelerating decomposition. Check with local authorities about the materials you use for temporary structure sidewalls, as certain materials may be prohibited in your area.

All compost piles (whether outdoor on in inside bins) must be placed on an all-weather surface, such as a plastic liner, asphalt or concrete, to prevent surface and groundwater contamination, and to ensure that you can access the facility year around.

If you’re in a region with high annual rainfall, consider adding a roof over compost piles to prevent excessive moisture from derailing the decomposition process. The temporary bale compost structure and compost windrows do not have static construction guidelines other than the sizing and siting considerations discussed in previous steps.

Then place the carcass flat on top of the compost mixture and at least 1 foot from the edge of the pile. Completely cover the carcass with about 12 inches of your chosen carbon source. Add water so that the pile is moist, but not soaked.

Repeat layers until the pile is about 6 feet high.

To compost or not?

Economic factors to consider

When deciding what to do with animal mortalities, especially when it comes to the cost of composting versus other disposal methods, keep in mind that it may be the most economical to use a combination of practices.

Small animals decompose more quickly, and there’s normally a higher mortality rate among youngstock than mature cattle, notes Dan Short, University of Wisconsin extension livestock agent in Dodge County, Wis. If your local rendering service charges $25 per head to pick up mortalities, it will cost you $25 per hundredweight for a 100-pound calf. However, that cost per hundredweight drops significantly for a mature cow — a 1,400-pound cow would cost $1.79 per hundredweight for pickup.

“If a dairy didn’t want to compost all of its dead animals, composting only the smaller youngstock carcasses may be the most cost-effective approach,” suggests Short.

Still, experiments in New Mexico found that on-farm mortality compost piles saved producers about $20 per head over the cost of rendering adult dairy cows. Plus, composting yields a fertilizer product that can be applied back to the land, thus reducing your fertilizer bill for crops.

Be sure to determine the cost-effectiveness of each disposal option for your dairy, since conditions and cost varies throughout the country.

A myriad of resources are available for animal carcass composting. Here is a short list:

“On-farm Composting Handbook” published through the Northeast Regional Ag Engineering Service/Cooperative Extension Service (NRAES). To order, call (607) 255-7643. Or visit the MidWest Plan Service Web site at: www.mwpshq.org